1. Field of the Invention
The present invention relates to slide fasteners, and more particularly to a slide fastener stringer having a continuous zigzag-shaped thermoplastic molded coupling element strip attached to a stringer tape along a longitudinal edge thereof.
2. Prior Art
Various slide fastener stringers are known in which a continuous zigzag-shaped strip of thermoplastic molded coupling elements is attached to a stringer tape along a longitudinal edge thereof. The successive coupling elements are interconnected by a plurality of thermoplastic molded connecting portions alternately disposed at opposite sides of the strip and extending one between each adjacent pair of the coupling elements. Because of relatively high rigidity of the thermoplastic connecting portions, the prior art stringers are poor in flexibility.
U.S. Pat. No. 3,328,857 discloses a continuous zigzag-shaped thermoplastic molded coupling element strip having thermoplastic connecting portions which are thin or slender in order to produce an increased degree of flexibility. In general, the slender connecting portions have only an insufficient degree of strength and hence tend to be easily broken or otherwise damaged when the stringer and thus the coupling element strip is bent in an edgewise direction during the opening and closing of a slide fastener. In the strip of U.S. Pat. No. 3,328,857, a flexible core thread is embedded in each series of the thermoplastic connecting portions through the full length of the strip, making the latter more flexible, but, on the other hand, causing each connecting portion to be in the form of a tube having a reduced thickness. Because of this small thickness of the tubular connecting portions, sufficient durability of the strip is difficult to achieve.